Increasing the sugar content of plants

ABSTRACT

The sugar content of plants is increased by a method in which the plants are treated, from 1 to 15 weeks prior to harvesting, with a compound of the formula (I) ##STR1## where R 1  is alkyl of 1 to 4 carbon atoms, R 2  is alkyl of 1 to 4 carbon atoms, unsubstituted or halogen-substituted alkenyl of 3 to 5 carbon atoms or alkynyl of not more than 5 carbon atoms, R 3  is a non-aromatic heterocyclic structure which has 5 to 7 ring members and no double bonds or one double bond in a heterocyclic ring, contains 1 or 2 hetero atoms from the group consisting of sulfur and oxygen, and can be substituted by alkyl of not more than 3 carbon atoms, and X is H or C00-alkyl, or one of its plant-tolerated salts.

The present invention relates to a method for increasing the sugar content of plants by treating them with a cyclohexane-1,3-dione derivative.

It has been disclosed that substituted cyclohexane-1,3-dione derivatives , possess herbicidal properties (German Laid-Open Applications Nos. DOS 2,439,104 and DOS 2,822,304 and European Pat. No. 71,707). Moreover, the herbicidal action is directed in particular against gramineous weeds, while many broad-leaved crops are not damaged.

It has also been disclosed that certain cyclohexanedione derivatives are capable of increasing the sugar content of various plants (European Pat. No. 47,972 and U.S. Pat. No. 4,334,913).

We have found that the sugar content of sugar cane or sweet sorghum can be reliably increased using a very small amount of active ingredient if the plants are treated, from 1 to 15 weeks prior to harvesting, with a compound of the formula (I) ##STR2## where R¹ is alkyl of 1 to 4 carbon atoms, R² is alkyl of 1 to 4 carbon atoms, unsubstituted or halogen-substituted alkenyl of 3 to 5 carbon atoms or alkynyl of not more than 5 carbon atoms, R³ is a non-aromatic heterocyclic structure which has 5 to 7 ring members and no double bonds or one double bond in the heterocyclic ring, contains one or two hetero atoms from the group consisting of sulfur and oxygen and may be substituted by alkyl of not more than 3 carbon atoms, and X is H or COO-alkyl, or one of its plant-tolerated salts.

R¹ is, for example, ethyl or propyl, R² is, for example, ethyl, allyl, chloroallyl, trichloroallyl, propargyl or propyl, R³ is, for example, tetrahydropyran-3-yl, 4-methyltetrahydropyran-3-yl, dihydropyran-3-yl, tetrahydrothiopyran-3-yl, dihydrothiopyran-3-yl, 1,4-dioxanyl or tetrahydropyran-4-yl, and X is, for example, methoxycarbonyl.

A plant-tolerated salt is, for example, an ammonium or alkali metal (sodium or potassium) salt.

The active ingredients used according to the invention can occur in a number of tautomeric forms, all of which are embraced by formula I: ##STR3##

The active ingredients can be obtained by reacting a compound of the formula ##STR4## where R¹, R³ and X have the above meanings, with a hydroxylamine derivative R² O--NH₃ Y, where R² has the above meanings and Y is an anion.

The reaction is advantageously carried out in a heterogeneous phase in an inert diluent at from from 0° to 80° C., or from 0° C. to the boiling point of the reaction mixture, in the presence of a base. Examples of suitable bases are carbonates, bicarbonates, acetates, alcoholates, hydroxides and oxides of alkali metals and alkaline earth metals, in particular of sodium, potassium, magnesium and calcium. It is also possible to use organic bases, such as pyridine or tertiary amines.

The reaction proceeds particularly well at a pH of 2 to 7, in particular from 4.5 to 5.5, the pH advantageously being established by adding an acetate, for example an alkali metal acetate, in particular sodium acetate or potassium acetate, or a mixture of the two salts. Alkali metal acetates are added in amounts of, for example, from 0.5 to 2 moles, based on the ammonium compound R² O--NH₃ Y.

Examples of suitable solvents are dimethyl sulfoxide, alcohols, such as methanol, ethanol or isopropanol, benzene, chlorohydrocarbons, such as chloroform or dichloroethane, esters, such as ethyl acetate, and ethers, such as dioxane or tetrahydrofuran.

The reaction is complete after a few hours, and the product can then be isolated by evaporating down the mixture, adding water and extracting with unpolar solvent, such as methylene chloride, and distilling off the solvent under reduced pressure.

The active ingredients may furthermore be obtained by reacting the compound of the formula II with the hydroxylamine of the formula R² O--NH₂, while R² has the above meanings, in an inert diluent at from 0° C. to the boiling point of the reaction mixture, in particular from 15° to 70° C.

Examples of suitable solvents for this reaction are alcohols, such as methanol, ethanol, isopropanol or cyclohexanol, hydrocarbons or chlorohydrocarbons, such as methylene chloride, toluene or dichloroethane, esters, such as ethyl acetate, nitriles, such as acetonitrile, and cyclic ethers, such as tetrahydrofuran.

The alkali metal salts of the compounds of the formula I can be obtained by treating the compounds with sodium hydroxide or potassium hydroxide in aqueous solution or in an organic solvent, such as methanol, ethanol or acetone. Sodium alcoholates and potassium alcoholates can also serve as bases.

The other metal salts, e.g. the manganese, copper, zinc, iron and barium salts, can be prepared from the sodium salts by reaction with the corresponding metal chloride in aqueous solution.

The compounds of the formula II can be prepared, using methods known from the literature (Tetrahedron Lett. 29 (1975), 2491), from cyclohexane-1,3-diones of the formula III, which may also occur in the tautomeric forms of formulae IIIa and IIIb ##STR5##

It is also possible to prepare compounds of the formula II via the enol-ester intermediates, which may be obtained as isomer mixtures in the reaction of compounds of the formula III and undergo rearrangement in the presence of imidazole or pyridine derivatives (Japanese Preliminary Publication No. 54/063052 ).

The compounds of the formula III are obtained by processes known from the literature, as can be seen from the scheme below: ##STR6##

The Example which follows illustrates the method of preparation of the active ingredients.

EXAMPLE

3.69 parts by weight of sodium acetate and 3.51 parts by weight of ethoxyammonium chloride were added to 10.0 parts by weight of 2-butyryl-5-(4-methyltetrahydropyran-3-yl)-cyclohexane-1,3-dione in 100 ml of ethanol, and the mixture was stirred for 20 hours at room temperature. To work up the mixture, it was poured into ice water and extracted with methylene chloride, and the organic phase was washed with water, dried and evaporated down to give 10.7 parts by weight of 2-(1-ethoxyaminobutylidene)-5-(4-methyltetrahydropyran-3-yl)-cyclohexane-1,3-dione (active ingredient No. 1); n_(D) ²² =1.5235.

C₁₈ H₂₉ NO₄ (molecular weight=323).

The compounds below (List 1) were prepared in a similar manner:

    __________________________________________________________________________     No.                                                                               R.sup.1                                                                              R.sup.2                                                                               R.sup.3       X     .sup.1 H--NMR data/n.sub.D /mp.                                                |°C.|             __________________________________________________________________________      2 Ethyl Ethyl  3-Tetrahydrothiopyranyl                                                                      H     n .sub.D.sup.25  = 1.5540                   3 Ethyl Allyl  3-Tetrahydrothiopyranyl                                                                      H     n .sub.D.sup.25  = 1.5644                   4 n-Propyl                                                                             Ethyl  3-Tetrahydrothiopyranyl                                                                      H     n .sub.D.sup.25  = 1.5588                   5 n-Propyl                                                                             Allyl  3-Tetrahydrothiopyranyl                                                                      H     n .sub.D.sup.25  = 1.5559                   6 n-Propyl                                                                             3-Chloroallyl                                                                         3-Tetrahydrothiopyranyl                                                                      H     n .sub.D.sup.22  = 1.5569                           (trans)                                                                7 n-Propyl                                                                             Ethyl  3-Tetrahydropyranyl                                                                          H     n .sub.D.sup.24  = 1.5149                   8 n-Propyl                                                                             Allyl  3-Tetrahydropyranyl                                                                          H     n .sub.D.sup.18  = 1.5313                   9 Ethyl Ethyl  3-Tetrahydropyranyl                                                                          H     mp.: 38-40° C.                      10 Ethyl Allyl  3-Tetrahydropyranyl                                                                          H     n .sub.D.sup.18  = 1 5342                  11 n-Propyl                                                                             Ethyl  4-Tetrahydropyranyl                                                                          H     mp.: 48-50°  C.                     12 n-Propyl                                                                             Allyl  4-Tetrahydropyranyl                                                                          H     mp.: 55-56° C.                      13 Ethyl Ethyl  4-Tetrahydropyranyl                                                                          H     δ = 1.35(t), 1.68(d), 3.35(t)        14 Ethyl Allyl  4-Tetrahydropyranyl                                                                          H     δ = 1.15(t), 2.95(g), 3.35(t),                                           4.50(d)                                    15 n-Propyl                                                                             Ethyl  3-Tetrahydrofuranyl                                                                          H     mp.: 36-39° C.                      16 n-Propyl                                                                             Allyl  3-Tetrahydropyranyl                                                                          H     n .sub.D.sup.29  = 1.5302                  17 n-Propyl                                                                             Ethyl  1,4-Dioxanyl  H     n .sub.D.sup.22  = 1.5226                  18 n-Propyl                                                                             Allyl  1,4-Dioxanyl  H     n .sub.D.sup.22  = 1.5229                  19 n-Propyl                                                                             3-     1,4-Dioxanyl  H     n .sub.D.sup.22  = 1.5391                  20 Ethyl Ethyl  1,4-Dioxanyl  H     n .sub.D.sup.21  = 1.5259                  21 Ethyl Ethyl  2-isopropyl-1,3-dioxepan-5-yl                                                                H     δ = 0.90(d), 1.14(t), 1.32(t),                                           4.30(m)                                    22 n-Propyl                                                                             Ethyl  2-isopropyl-1,3-dioxepan-5-yl                                                                H     n .sub.D.sup.26  = 1.514                   23 n-Propyl                                                                             Ethyl  3-Tetrahydrothiopyranyl                                                                      COOCH.sub.3                                                                          n .sub.D.sup.22  = 1.5431                  24 Ethyl 3-Chloroalkyl                                                                         3-Tetrahydropyranyl                                                                          H     n .sub.D.sup.22  = 1.5480                           (trans)                                                               25 Ethyl 3-Chloroalkyl                                                                         4-Tetrahydropyranyl                                                                          H     1.1(t),3.4(t), 4.5(d)                               (trans)                                                               26 n-Propyl                                                                             3-Chloroalkyl                                                                         "             H     n .sub.D.sup.19  = 1.5407                           (trans)                                                               27 Ethyl 3-Chloroalkyl                                                                         3-Tetrahydrofuranyl                                                                          H     mp. = 50-52° C.                              (trans)                                                               28 n-Propyl                                                                             3-Chloroalkyl                                                                         "             H     mp. = 55° C.                                 (trans)                                                               29 n-Propyl                                                                             3-Chloroalkyl                                                                         3-Tetrahydrothiopyranyl                                                                      H     n .sub.D.sup.22  = 1.5669                           (trans)                                                               30 "     Methyl "             H     0.95(t), 2.9(t), 3.85(s)                   31 "     n-Propyl                                                                              "             H     n .sub.D.sup.22  = 1.5437                  32 "     Propargyl                                                                             "             H     n .sub.D.sup.21  = 1.5621                  33 Ethyl "      "             H     n .sub.D.sup.21  = 1.5676                  34 "     n-Propyl                                                                              "             H     mp.: 54-56° C.                      35 n-Propyl                                                                             Ethyl  "             COOCH.sub.3                                                                          n .sub.D.sup.22  = 1.5431                  36 "     Allyl  "             COOCH.sub.3                                                                          n .sub.D.sup.22  = 1.5468                  37 2-Methyl-                                                                            Ethyl  "             H     0.85(d), 2.9(d), 4.10(t)                      propyl                                                                      38 2-Methyl                                                                             Allyl  "             H     n .sub.D.sup.23  = 1.5594                     propyl                                                                      39 2-Methyl-                                                                            Methyl "             H     n .sub.D.sup.23  = 1.5600                     propyl                                                                      40 n-Butyl                                                                              Ethyl  "             H     n .sub.D.sup.23  = 1.5447                  41 "     Allyl  "             H     n .sub.D.sup.23  = 1.5500                  42 n-Propyl                                                                             Isopropyl                                                                             "             H     1.3(d) 4.25(pept)                          43 "     Isobutyl                                                                              "             H     0.95(d + t) 2.9(q) 3.8(d)                  44 "     2-Methyl-2-                                                                           "             H     4.4(s) 5.05(s)                                      propen-1-yl                                                           __________________________________________________________________________

The following compounds were also prepared:

    ______________________________________                                         No.                                                                            ______________________________________                                         45       sodium salt of compound 4                                             46       potassium salt of compound 4                                          47       magnesium salt of compound 4                                          48       calcium salt of compound 4                                            49       tetramethylammonium salt of compound 4                                50       trimethylbenzylammonium salt of compound 4                            51       trimethylsulfenium salt of compound 4                                 52       trimethylsulfoxenium salt of compound 4                               53       aluminum salt of compound 4.                                          ______________________________________                                    

Application of the conventional active ingredients as herbicides is usually carried out in practice from 10 to 30 days after emergence of the crops, the application rates being from 0.1 to 1 kg/ha of active ingredient. Under these conditions, the grasses (Gramineae) are substantially destroyed.

It is surprising that, for example, sugar cane plants, which belong to the Gramineae family, are not damaged in the method according to the invention, where the active ingredients are applied in amounts of from 1 to 1,000 g of active ingredient per ha from 1 to 15 weeks prior to harvesting.

The application rates can vary within wide limits, for example from 1 to 1,000, in particular from 10 to 1,000, preferably from 20 to 500, g/ha of active ingredient. The total amount used can be applied in a single dose or in two part doses.

According to the invention, the plants are treated from 1 to 15, in particular from 1 to 13, preferably from 1 to 12, weeks prior to harvesting. It may be advantageous to use conventional formulation assistants and possibly a wetting agent.

The Examples which follow illustrate the method according to the invention.

The polarization is the rotation of polarized light in the crude sap of the sugar-containing plants, this rotation being due to the presence of optically active compounds, including sucrose, in the sap.

Sucrose is the content of cane sugar in the crude sap, expressed as a percentage by weight.

Purity is the content of sugar in the constituents dissolved in the crude sap, expressed as a percentage by weight. All values stated in the Examples were determined on the day of harvesting.

EXAMPLE 1 Saccharum officinarum, variety CB 4789 Treatment: 5 weeks prior to harvesting (analysis) on first year sugar cane plants

    ______________________________________                                                             Polarization                                                         g/ha of active                                                                           sucrose    Purity                                                    ingredient                                                                               %          %                                               ______________________________________                                         Untreated    0          13.6       86.7                                        Compound No. 1                                                                             300         13.9       88.3                                        Comparison* 900         13.4       86.2                                        ______________________________________                                          *The comparative agent is the compound of Example VII of European Patent       47,972.                                                                  

The sugar cane stems harvested representatively by the conventional experimental methods were analyzed in the laboratory according to the known standard guidelines. The result shows an increased sucrose content coupled with higher sap purity. This shows that there is a direct influence which increases the sugar yield.

Compound No. 1 increases the sugar yield compared with untreated pieces as well as with the pieces treated with the comparative active ingredient.

EXAMPLE 2 Saccharum officinarum, variety CP 6 3-588

Treatment: 4 weeks prior to harvesting (analysis) on first year sugar cane plants

    ______________________________________                                                  g/ha of Polariza-                                                                               Puri-   Sugar yield,                                          active  tion su- ty***   kg of sugar/                                          ingredient                                                                             crose %  %       tonne of cane                                ______________________________________                                         Untreated   0        13.0     100   280.0 = 100                                Compound No. 4                                                                            28        14.2     100.5 110                                                   112       14.5     101.0 112                                        Comparison*                                                                               56        13.2     94.2  99                                         Comparison**                                                                              3360      14.5     99.4  111                                        ______________________________________                                          *The comparison is the active ingredient of Example VII of European Paten      47,972                                                                         **The comparison is the active ingredient glyphosine                           [N,N--bis(phosphonomethyl) glycine], cf. U.S. Pat. No. 3,455,675               ***After conversion to standard conditions (aftertreated = 100)          

The experiment was evaluated similarly to Example 1. At both application rates, Compound No. 4 increased the sucrose content as well as the sap purity. The resulting sugar yield was increased by from 10 to 12% compared with untreated pieces. The action is similar to that of the standard, although the latter has to be used in a dose which is from 30 to 120 times higher in order to obtain a satisfactory result.

EXAMPLE 3 Saccharum officinarum, variety CP 63-588

Treatment: 8 weeks prior to harvesting (analysis) on first year sugar cane plants

    ______________________________________                                                  g/ha of Polariza-        Sugar yield,                                          active  tion suc-                                                                               Purity  kg of sugar/                                          ingredient                                                                             rose %   %       tonne of cane                                ______________________________________                                         Untreated  28        13.4     96.5  284.9 = 100                                Compound No. 4                                                                            28        14.0     98.0  105                                                   112       14.5     100.0 110                                        Comparison*                                                                               56        13.3     94.0  98                                         Comparison**                                                                              3,360     14.2     98.4  107                                        ______________________________________                                    

The experiment was evaluated similarly to Example 1. At both application rates, Compound No. 4 increased the sucrose content and the sap purity, giving a sugar yield 5-10% higher than that of the untreated pieces. In this case too, Compound No. 4 is similar to the standard, although the latter has to be applied in an amount which is from 30 to 120 times higher in order to obtain a satisfactory result. 

We claim:
 1. A method for increasing the sugar content of sugar producing plants, wherein the plants are treated, from 1 to 15 weeks prior to harvesting, with an effective amount of a compound of the formula (I) ##STR7## where R¹ is alkyl of 1 to 4 carbon atoms, R² is alkyl of 1 to 4 carbon atoms, unsubstituted or halogen-substituted alkenyl of 3 to 5 carbon atoms or alkynyl of not more than 5 carbon atoms, R³ is a tetrahydropyranyl or a tetrahydrothiopyrnanyl substituent, and can be substituted by alkyl of not more than 3 carbon atoms, and X is H or COO-alkyl, or one of its plant-tolerated salts.
 2. A method as defined in claim 1, wherein the plant is sugar cane (Saccharum officinarum) or sweet sorghum (Sorghum saccharatum).
 3. A method as defined in claim 1, wherein the plants are treated with from 1 to 1,000 g/ha of active ingredient.
 4. The method of claim 1, wherein R³ is selected from the group consisting of 3-tetrahydrothiopyranal, 3-tetrahydropyranyl and 4-tetrahydropyranal.
 5. The method of claim 1, wherein R¹ is n-propyl, R² is ethyl and R³ is 3-tetrahydrothiopyranyl.
 6. The method of claim 1, wherein R³ is 4-methyltetrahydropyran-3-yl.
 7. The method of claim 3, wherein the plants are treated with from 20 to 500g/ha of active ingredient.
 8. The method of claim 1, wherein the plants are treated from 1 to 12 weeks prior to harvesting. 